With the advent of resists for KrF excimer laser light (248 nm), an image forming method utilizing the so-called chemical amplification has been adopted for the purpose of making compensation for sensitivity reduction caused by light absorption under image formation using the resists. To illustrate by a positive image forming method utilizing chemical amplification, the positive image forming method is a method in which light exposure is performed and thereby decomposition of an acid generator is induced in exposed areas to generate an acid, then baking after the exposure (or PEB: Post Exposure Bake) is performed and thereby alkali-insoluble groups are converted into alkali-soluble groups with the aid of the generated acid as a reaction catalyst, and further alkali development is performed and thereby the exposed areas are removed. At present, the positive image forming method utilizing such a chemical amplification mechanism is in the mainstream, and it has also been known that the method was used for forming e.g. contact holes (see WO 2008/149701, JP-A-2004-361629 (the term “JP-A” as used herein means an unexamined published Japanese patent application)).
Although the positive image forming method can form a good-quality pattern of isolated lines or dots, isolated spaces (a pattern of trenches) or a pattern of fine holes formed by using the positive image forming method tends to suffer degradation in pattern profile.
Still finer patterning has been required in recent years, and quite recently a technique of forming negative images through the resolution of a resist film made from a chemical amplification negative resist composition by the use of an organic developer (see e.g. JP-A-2008-292975) has also been known in addition to the technique of forming positive images through the use of chemical amplification positive resist compositions currently in vogue.
With respect to the technique of forming negative images through imagewise resolution of a resist film by the use of an organic developer, there has been known a technique in which a resist film containing an acid generator capable of generating an acid is resolved imagewise with an organic developer to form a pattern, then the resulting resist film is coated with a material for forming a crosslinked layer (also referred to as a crosslinked-layer forming material) to become insoluble in a developer through reaction in the presence of an acid, the acid in the resist pattern is made to diffuse to the crosslinked-layer forming material via an additional treatment process such as a heating process, and thereby a layer insoluble in a developer is formed at the interface between the crosslinked-layer forming material and the pattern, and dimensions of the resist pattern is enlarged to result in effective reduction of trench dimensions or hole dimensions. And it has been reported that such a technique allowed formation of a pattern of trenches or holes whose dimensions were effectively made finer without leaving scum (see JP-A-2008-310314).